The major goal of this work is to understand the mechanisms involved in the active membrane transport of organic cations such as choline and catecholamines and drugs such as morphine and to understand the role of kidney transport in the regulation of the plasma levels of choline. Bidirectional transport of the organic cation choline has been determined by in vivo clearance studies and by in vivo micropuncture studies. These findings will be extended by the study of the isolated perfused tubule segments in vitro from rabbits. The effect of choline and catecholamines on the renal exccetion of inorganic cations such as Na, K, Cl, HCO3, HPO4 and H ion will be observed using the Sperber technique in chickens. In this way the direct effect of these cations can be assessed on electrolyte transport independent of the effects of changes in blood flow.